ALBANY – Sen. Charles Schumer is among the Senate’s biggest money-wasters when it comes to office expenditures, having even treated his staff to a “retreat” at a lavish upstate resort, his Republican opponent charges.

Schumer’s office spent more than $21,000 for a three-day retreat at the Beaver Hollow Conference and Training Center in western New York in November 2002, according to documents provided to The Post by the campaign of upstate Assemblyman Howard Mills. Schumer spokesman Stu Loeser said the retreat was for 60 Schumer staffers who work in nine offices.

“Every good organization does these kinds of meetings,” he said. “They are low-budget, off-season working meetings where people shared rooms and the total cost was only about $300 per person.”

Schumer also held a two-day staff retreat in Maryland in 1999 that cost taxpayers about $10,000, according to the documents provided by the Mills camp.

Meanwhile, Senate documents show that Schumer ranked third in the Senate in travel expenses, shelling out nearly $84,000 during the six-month period beginning last Oct. 1 and ending March 31, according to the documents.

His total on travel was about $24,000 more that of Sen. Hillary Rodham Clinton and exceeded the delegations of 37 states, the numbers show.

Schumer, meanwhile, ranked fifth-highest in rent, communications and utilities, third-highest for supplies and materials, seventh in payroll and fifth in net office expenditures.

“This spending is just another example of Chuck Schumer’s blatant disregard for the taxpayers of the state of New York,” Quartararo said.

Schumer aides dismissed the findings as “ludicrous,” saying the Senate’s Republican leadership not only sets his office budget, but that Schumer ranks 30th in the Senate in percentage of his total budget spent.